The present invention relates to a method for manufacturing magnetic tape cassette, particularly, a magnetic tape cassette the half portions of the body of which are manufactured using an image transfer molding process.
A conventional magnetic tape cassette includes upper and a lower half portions between which are rotatably supported a pair of tape hubs. Each of the half portions is manufactured from a plastic or the like using an injection molding process. After injection molding, paper or the like carrying a prescribed design is adhered to the outside surface of the half portion, or a design is directly printed on the half portion, to thereby enhance the appearance of the cassette. However, since the manufacture of the half portion requires injection molding of the plastic or the like and a subsequent step of adhering the paper or the like or the printing of a design on the outside surface of the half portion, the process is relatively complicated.
To solve this problem, an image transfer molding process in which the prescribed design is printed on the outside surface of the half portion during the injection molding process has been developed, as disclosed in Japanese Unexamined Published Utility Model Applications Nos. 113281/88 and 118782/88. In the image transfer molding process, molten plastic or the like is injected through a gate communicating with a cavity formed between a pair of dies for molding the half portion, and an image layer on a base film disposed in the cavity in advance is transferred onto the outside surface of the half portion by the pressure and heat of the injected molten plastic material. With this process, the manufacture of the half portion is simplified, thereby lowering the cost of the magnetic tape cassette.
In another magnetic tape cassette, the outside surface of each half portion of the body is provided with a roughened part during image transfer molding. Such a cassette is disclosed in Japanese Unexamined Published Utility Model Application No. 2282/88. The roughened part of the outside surface of the cassette body can be written on with an ordinary writing instrument.
In the magnetic tape cassette disclosed in Japanese Unexamined Published Utility Model Application No. 2282/88, an ink layer, which contains pigment grains each having a diameter of about 3 to 10 .mu.m, for example, and is to form an image transfer matte part, is provided as a part of the outside surface of an image transfer layer. The image transfer layer is composed of an adhesive layer, an ink layer, etc., which are shifted onto the outside surface of the half portion of the body of the cassette upon the injection of the molten plastic in to the molding cavity so that the ink layer containing the pigment grains constitutes the roughened part of the outside surface of the half portion. However, if such an ink layer containing pigment grains is provided on the entire outside surface of the half portion, the thickness of the overall image transfer layer is unavoidably increased. In image transfer molding, molten plastic is injected into a molding cavity through which are inserted pins provided in order to form holes such as reference holes, capstan holes and screw holes in the half portion of the cassette body. These pins unavoidably pinch the base film bearing the image transfer layer thereon. After the plastic injected into the cavity has solidified, the half portion is extracted from the dies. The base film is then peeled from the surface of the half portion and the image transfer layer is left on the surface of the half portion. Therefore, if the entire outside surface of the half portion is roughened (matted) in the above-described manner wherein the thickness of the image transfer layer is increased, the parts of the image transfer layer pinched by the pins are likely to be left as residual thin films in the holes of the half portion or stuck to the other parts of the image transfer layer on the outside surface of the half portion. The image transfer layer parts left as residual thin film segments must be removed after the image transfer molding of the half portion. This is a problem.